This invention relates to fiberization of thermoplastic materials, particularly glass; and the invention is concerned with equipment employing gas streams of blasts for the purpose of effecting attenuation of thermoplastic materials in attenuable condition, for instance, effecting fiberization of molten glass.
Although the invention is applicable to the fiberization of a variety of materials, especially thermoplastic materials, the invention is particularly useful in connection with formation of fibers from molten glass; and for this reason, much of the following description refers to the formation of fibers from glass.
In various gas blast attenuation techniques, a blast nozzle is employed for delivery of the attenuating gas stream; and provision is made for delivering a stream of the molten material into the blast delivered from the nozzle, it being preferred that the point of delivery of the molten material into the gas stream should be relatively close to the orifice from which the blast or attenuating gas stream is delivered.
The close proximity of the point of delivery of the attenuable material to the discharge orifice is of importance in order to make maximum use of the energy of the attenuating blast. However, the close proximity of the point of entrance of the attenuable stream into the blast to the blast nozzle has a tendency under certain conditions to result in undesirable contact of portions of particles of the glass stream with the nozzle structure. Indeed, this sometimes results in build-up of deposits of molten material on the nozzle, with consequent periodic delivery of portions of such deposits into the region of attenuation in the gas blast. In turn, this has a tendency to build up undesired particles or "shot" in the fibrous product being made.
One of the principal objects of the invention is to provide an arrangement providing for delivery of the molten stream into the gas blast in a zone very close to the blast discharge orifice, while at the same time, minimizing contact of the molten stream or particles thereof with the nozzle structure.
For the above purposes, the invention contemplates the employment of a blast nozzle having a convexly curved surface adjacent to one side of the discharging blast, together with a glass supply means delivering a molten stream to the blast in the region of said convexly curved surface. Provision is also made for the flow, preferably laminar flow, of air or gas over the convexly curved surface in a direction approaching the discharge orifice of the blast. In this way, a Coanda effect is developed along the convexly curved surface of the blast nozzle lip; and this flow aids in maintaining the molten stream out of contact with the blast nozzle lip, as the molten stream is delivered into the blast, even when the region of delivery is quite close to the blast nozzle, as is desirable.
In a preferred embodiment, as fully described hereinafter and illustrated in the drawings, the action above described is further enhanced by the employment of a secondary jet or gas stream for each stream of molten material, the secondary jets being delivered in paths approaching the convexly curved Coanda surface of the blast nozzle lip, and thereby enhancing the development of the Coanda action over the curved surface of the nozzle lip. In this preferred embodiment, individual streams of attenuable material, for example, molten glass, are delivered initially into the influence of the secondary jets, the streams of molten material being carried by the jets into the region of the Coanda flow over the blast nozzle lip and thence into the blast itself for attenuation.
It is also contemplated in accordance with the invention that the secondary jets be subjected to the influence of a deflector of the kind fully disclosed in Lavecque et al U.S. Pat. No. 4,102,662, issued July 25, 1978. This type of deflected secondary jets provides a zone of laminar flow in each jet into which the associated stream of molten material is initially delivered.
The foregoing arrangements provide for minimization of undesirable deposits on the blast nozzle lip, even when the various components of the fiberizing system are brought very close together, as is frequently desirable in order to make maximum use of the energy expended in operating the system, and thereby correspondingly reduce the overall cost of fiber production.